Induction furnace



Patented June 7, 1932 UNITED STATES PATENT OFFICE I THOMAS H. LONG, OF IRWIN PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA INDUCTION FURNAGE Application led October, 1930. Serial 'Nm 486,582.

.My invention relates to electric furnaces and particularly to electric induction furnaces.

An object of my invention is to provide .a

plural-layer plural-turn energizing coil which shall be so designed as to have a mimmum amount of energy loss therein.

Another object of my invention is to provide an energizing coil for an inductive heating device in which the conductors are of different shapes and dimensions and are properly coordinated to facilitate assembling them and embody also a Huid-cooling means for each group. Y

In practicing my invention, I provide an energizing-coil structure in which the conductor nearest to the axis of the coil or, more particularly, nearest to the material being heated by the coil, will have a minimum radial thickness, as well as a maximum axial thickness, the radial thickness increasing in the other turns while the axial thickness decreases. A final outside conductor is preferably fluid cooled. f

In the drawing,

Figure 1 is a view, in vertical section, of a portion of a crucible with which is associated a plural-turn plural-layer energizing coil embodying my invention,

80 Fig. 2 is a view, in perspective, of one conductor constituting, at the same time, a heat shield for the other conductors, and,

Fig. 3 is a view, in lateral section, through a group of conductors, the heat shield being omitted.

It is highly desirable, in inductive heating devices, that means be provided in the energizing coil and, more particularly, in the conductors, to reduce the eddy-current losses 40 therein to as eat an extent as possible. It is also desira le to provide some form of heat shield between the energizing coil and the material which is being heat treated.

Referring more particularly to Fig. 1 of the drawing, I have there illustrated, in part only, a crucible 11 which is intended to represent any device ormaterial to be heated or to be heat treated. Thus, the crucible 11 may be employed to contain material to be melted, or, in

5 place of the Crucible, a block of meta-l or some other material to be heated may be located within an energizing coil to be hereinafter described. In order to protect, to as great an extent as possible, the electric conductors of the energizing coil, I may provide a sheet of solid electric insulating material 12 between the material being heated and the energizing coil and this sheet may be in the form of an annulus or cylinder oi' mica.

An energizing coil, located around the so Crucible 11, includes a plurality of sets of turns and layers individually designated by the numerals 13, 14, 16 and 17, each set including avplurality of turns and layers of conductors of diiierent dimensions and shapes. Thus, I provide a conductor 21, whlch is of relatively small dimension, radially of the coil, and is relatively wide in a direction axially of the coil. The next two turns are in the shape of rectangular con- 7o ductors 23 and 24, each of which is somewhat thicker radially of the coil than is the conductor 21 and each of which is slightly less than one-half of the axial width of the conductor 21.

Next in the radially outward order vare located three conductors 26, 27 and 28, each of which is of greater radial thickness than the conductors 21, 28 and 24, but is of lesser axial width than those conductors. In fact, the dimensions axially of the coil have been so selected as to be slightly less than one-third the width oi' the conductor 21 axially of the coil, the dimensions being made slightly less than one-third in order to permit of locating electric-insulating material between them. Outermost in the set or group, is located a tubular conductor 29, the axial width of which is substantially the same as that of conductor 21, that of both conductors 23 and 90 and that of the three conductors 26, 27 and In order to provide a heat shield and heatconducting member associated with each set of conductors, as hereinbefore described and as shown more particularly in Fig. 3 of the drawing, I provide another member which is made of electric-conducting material and which is shown in perspective in Fig. 2 of the drawing, and is designated by numeral 3l. The innermost portion of the member 31, designated by numeral 32, is located inside of conductor 21 and is of slightly less radial thickness than that conductor. `This l part of the member 3l constitutes a currentconducting portion, and is, therefore, made substantially continuous. Radially and outwardly extending portions 33 and 34, coextensive and integral with the portion 32, are provided, and are of such length as to permit their outer ends to be bent-over to form portions 36 and 37 which are located in close operative engagement with the outside portion of conductor 29. It is obvious that heat radiated or conducted from the material being heated or otherwise heat treated by inductive action of a current traversing the energizing coil, will irst reach the wall 32, and will be conducted by the portions 33 and 34 and the portions 36 and 37 to the tubular member 29, which, as has already been noted, may be traversed by a cooling fiuid to reduce the temperature of itself and also that of the heat screen 32 and that of the conductors located between conductors 21 and 29.

Electric-insulating material 38 is shown as being provided to properly electrically insulate the conductors from one another, in a manner well known in the art.

If the portions 33 and 34 of member 3l were made continuous, the temperature rise therein would be excessive because of eddycurrent loss therein, and, in order to reduce the eddy-current loss and, consequently, the temperature rise, I provide a plurality of radiallyv extending slits or slots 39 which extend through the parts 33 and 36 and the parts 34 and 37, respectively, as is shown more particularly in Fig. 2 of the drawing. The number of slots 39 may be any suitable or desired one, as may be found necessary, in actual practice, to maintain the eddy-current loss in the respective relatively narrow portions of the )arts 33 and 34 at a relativelyA low value.

T e conductors hereinbefore described may be connected in series-circuit relation to each other, as by making the innermost conductor 32 a helix of five turns and connecting one end thereof to the beginning of conductor 23, then connecting its other end to the beginning of conductor 24, and so on through all of the respective conductors in the coil, and, as this constitutes no particular part of my present invention, I have elected not to illustrate or describe the same.

In an energizing coil of the kind illustrated in Fig. l of the drawing, the axial magnetic flux density is greatest in the radial portion of conductor 32, and hence, this conductor has been made of the least radial thickness. The axial magnetic flux density is less at the radial distance of conductor 29, and hence, this conductor may have the greatest radial thick- 55 ness.

The device embodying my invention thus provides a relatively simple form of energizing coil for an inductive heating device in which different shapes and sizes of conductors are so combined in groups or sets of conductors as to permit manufacturing the same and connecting them in proper electriccircuit relation to a source of supply of electric energy, and in which the dimensions of the respective conductors shall be such as to result in a minimum eddy-current loss in the conductors themselves.

The use of a radially-slotted heat shield and current-conducting member ensures efcient cooling of the solid conductors by a single tubular current-conducting member.

Since various modifications may be made in thedevice embodying my invention without departing from the spirit and scope thereof, I desire that only such limitations shall be placed thereon as are imposed by the prior art or are set forth in the appended claims.

I claim as my invention:

l. In an electric-inductive heating device, a plural-layer energizing coil including conductors, the radial thickness of which increases with the distance between the respective layers and that layer in which there exists the maximum lux density.

2. In an electric-induction heating device, a plural-layer energizing coil, the number of turns of conductors per layer increasing inversely relative to the axial magnetic-linx density.

3. In an electric-induction heating device, 100 a plural-layer energizing coil, the radial thickness of the conductors of which increase with the distance of the conductor from the axis of the coil.

4. In an electric-inductive heating device, 105 an energizing coil, a thermal screen of relatively high heat conductivity located between the major portion of the coil and the material being inductively heated, and fluid-traversed cooling means for the thermal screen located 110 in a region of low magnetic-flux density.

5. In an electric-inductor heating device,

a plural-turn and plural-layer energizing coil in inductive relation to material being heated,

a Huid-traversed cooling member at that side 115 of each turn that is farthest away from the material being heated, a thermal screen between a part of the coil and the material being heated and constituting one of said layers, and heat-conducting means between the thermal screen and the fluid-traversed cooling member, said heat-conducting means being in heat-conducting relation to the intermediate layers of conductors.

6. In an electric-inductive heater, an energizing coil having a plurality of conductor turns, a thermal screen, a cooling member operatively and thermally associated with the thermal screen, both said thermal screen 1:0

and said cooling member constituting parts of the energizing-coil winding.

7 In an electric-inductive heating device, a plural-turn and plural-layer energizing coil, a thermal screen at one side of each turn between a part of the turn and the material to be heated, a fluid-traversed coolingmember on the other side of the turn, and heatconducting means extending from the thermal screen to the cooling member in a substantially radial plane, said heat-conducting means being radially slotted to reduce its own eddy-current loss.

8. In an electric-induction heater, a pluralturn and plural-layer energizing coil including a plurality of layers of solid electric conductors, the radial thickness of which decreases toward the axis of the coil, a iiuidconducting tubular member on the outside o of, and co-extensive with, each turn, and electric insulating material around and between the solid conductors and the tubular member of each turn.

9. In an electric-induction heater, a pluralturn and plural-layer-per-turn energizing coil including a plurality of layers of solid electric conductors, the radial thickness of which decreases toward the axis of the coil, a fluid-conducting tubular member on the outside of, and co-extensive with, each turn,

electric-insulating material around and between the solid conductors and the tubular member of each turn, and heat-conducting means operatively connecting the tubular member and the solid electric conductors to abstract heat therefrom.

10. In an electric-induction heating device for heating material, an energizing coil having a plurality of turns of current-traversed conductors and including a thermal screen between a portion of the coil turns and the material being heated.

11. A device as set forth in claim 7 in which the heat-conducting means is integral with the thermal screen.

12. A device as set forth in claim 7 in which the number of conductors per layer increases inversely relatively to the axial magnetic flux density.

5g 13. A device as set forth in claim 7 in which the radial thickness of the conductors of the coil increases with the distance of the conductor from the axis of the coil.

In testimony whereof I have hereunto subscribed my name this first day of October,

THOMAS I-I. LONG. 

